Power distribution panelboard

ABSTRACT

Plug-on enclosed fusible switches, enclosed lug devices and non-enclosed molded case circuit breakers are attached to a panelboard in a single or side-by-side double row. Spring biased latches retain the devices to the panelboard. Locating notches on the panelboard locate the devices at incremental spacing to provide a variable, compact arrangement for the devices. Filler plates and end structures on the devices cooperate with a cover for the panelboard to provide an integral dead front. The panelboard is particularly adapted for field assembly, including attachment of a main feed device which effects a plug-on feed in either a single or electrically parallel double panel arrangement.

This application is a division of copending application Ser. No.07/035,405, filed Apr. 7, 1987, in the name of Howard E. Koslosky et alfor Power Distribution Panelboard, and now U.S. Pat. No. 4,744,003.

BACKGROUND OF THE INVENTION

This invention relates to power distribution panelboards that areparticularly well suited for field assembly. It further relates to suchpanelboards which accept plug-in enclosed fusible switches and plug-inmolded case circuit breakers in the same panelboard, and which furtheraccept plug-in enclosed lug main units.

Panelboards are known which accept plug-in molded case circuit breakersof varying sizes and ratings, or which accept both enclosed fusibleswitches and circuit breakers when the circuit breaker is providedwithin a metallic box enclosure similar to the enclosure of the fusibleswitch. It is also known to provide panelboards which may be distributorstocked as separate parts and, to a limited extent, field assembled toone of several predetermined arrangements of circuit breakers and/orenclosed fusible switches. While the known panelboards have generallybeen satisfactory for their intended purposes, they have requireddistributors to maintain a large inventory of individual parts includingfactory assembled panels and main power feed devices. Additionally,versatility in the arrangement of circuit breakers and/or enclosedfusible switches has been limited.

SUMMARY OF THE INVENTION

This invention provides a panelboard which may be factory assembled orfield assembled from relatively few distributor stocked parts toaccommodate numerous arrangements of circuit breakers and/or enclosedfusible switches. The panelboard may comprise either single or doublesets of bus bars to accommodate single or double rows of switches,circuit breakers or lug units. Double bus embodiments are electricallyconnected in parallel for increasing the electrical capacity of thepanelboard by attaching a main circuit breaker, main switch or lug mainunit which has plug-on connectors for connecting to corresponding busbars of each set. Each breaker, switch or lug unit is electricallyconnected to the bus bars by a plug-on connection. Each device isfurther provided with at least one forwardly extending end structure tocooperate with a cover for the panelboard to provide a dead front forthe panelboard. The panelboard has vertically spaced locating notcheswhich cooperate with formations on the respective plug-on devices forlocating the devices at incremented intervals along the panelboard.Latches carried by the plug-in devices cooperate with notches inmounting rails of an interior frame assembly of the panelboard to securethe respective unit in its plugged-on condition. Insulators for mountingbus bars of the panelboard are provided in a predetermined length to bearranged in a stacked, end-to-end relationship on the interior frame toprovide overall lengthwise support for the bus bars in heights which arerelated to the incremented intervals for receiving the plug-on devices.The interior frame assembly may be reversed end-for-end to locate aneutral connector assembly, which is mounted thereto, at either theupper or lower end of the panelboard, and is arranged to receive wireshorizontally for reducing the amount of wire bending space requiredwithin the panelboard. These and other features and advantages of thepanelboard of this invention will become more readily apparent whenreading the following description and claims in conjunction with theaccompanying drawings.

Brief Description of the Drawings

FIG. l is a front view of the panelboard of this invention with a frontcover and door partially broken away from an enclosure of thepanelboard;

FIG. 2 is a front view of a twin interior frame assembly of thepanelboard of this invention;

FIG. 3 is a cross-sectional view of a neutral connector assembly of thepanelboard of this invention taken along the line 3--3 of FIG. 2;

FIG. 4 is a cross-sectional view of a single interior frame assemblytaken along the line 4--4 of FIG. 2 showing a set of bus bars mounted toa support insulator and the insulator mounted to the interior frame;

FIG. 5 is an exploded perspective view of a set of bus bars and asupport insulator showing the method of assembling the bus bars withinthe support insulator;

FIG. 6 is a top plan view of a support insulator;

FIG. 7 is a cross-sectional view of the support insulator taken alongline 7--7 of FIG. 6;

FIG. 8 is a cross-sectional view taken along line 8--8 of FIG. 1 showinga plug-on lug main unit having electrical connection with each bus barset of a twin interior frame for electrically connecting the respectivebus bar sets in parallel;

FIG. 9 is a cross-sectional view taken along line 9--9 of FIG. 1 showinga single molded case circuit breaker mounted to the right interior frameassembly and a filler plate arrangement for the single circuit breaker;

FIG. 10 is a cross-sectional view taken along line 10--10 of FIG. 1showing a pair of molded case circuit breakers mounted to the respectiveleft and right interior frames of the twin interior frame assembly;

FIG. 11 is a cross-sectional view taken along line 11--11 of FIG. 1showing a molded case circuit breaker embodied in a twin plug-on unitwhich mounts across both sides of the twin interior frame assembly andelectrically connects to both sets of bus bars;

FIG. 12 is a cross-sectional view taken along line 12--12 of FIG. 1showing a fusible switch unit mounted to the right side of the twininterior frame assembly and a lug unit mounted to the left side of thetwin interior frame assembly across from the above mentioned switchunit;

FIG. 13 is a cross-sectional view taken along line 13--13 of FIG. 1showing a twin fusible switch unit which mounts across both sides of thetwin interior frame assembly, but electrically connects to only one setof bus bars;

FIG. 14 is a side elevation view of a latch assembly of the plug-ondevices showing a segment of the device and the panelboard interiorframe in cross-section;

FIG. 15 is a bottom view of the latch assembly of FIG. 14 taken in thedirection of arrows 15--15 and showing a portion of the panelboardinterior frame in cross-section;

FIG. 16 is a perspective view of a fragmentary portion of the interiorframe showing locating notches and latch openings therein;

FIG. 17 is a view taken in the direction of the arrows of line 17--17 ofFIG. 1 showing a lower end cover for the interior frame assembly;

FIG. 18 is a cross-sectional view taken along line 18--18 of FIG. 1showing a top cover for the interior frame assembly covering the neutralconnector assembly; and

FIG. 19 is a cross-sectional view of a single interior frame panelboardshowing a deadfront flange attached to the cover.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A power distribution panelboard constructed in accordance with thisinvention is shown in front elevation in FIG. 1. The panelboardcomprises a box-shaped enclosure 2 having a rear panel 2a from whichside walls 2b, an upper wall 2c and a lower wall 2d extend forwardly toestablish a predetermined depth for the enclosure. The forward ends ofsidewalls 2b are formed over at right angles to provide forward flanges2e. Similarly, upper wall 2c and lower wall 2d are formed over toprovide forward flanges 2f and 2g, respectively. The flanges 2e, 2f and2g establish an open front in a common plane for enclosure 2. A cover 4is mounted to the front of enclosure 2 by a plurality of screw operatedhidden trim clamps similar to the clamp disclosed in U.S. Pat. No.3,116,081 issued Dec. 31, 1963 to L. G. Goodridge. These clamps, ofwhich only the operating screws 4a are shown, engage the rear surfacesof flanges 2e, 2f and 2g to clamp cover 4 tightly against the frontsurfaces of the flanges. In an alternate embodiment (not shown) thecover may comprise separate upper, lower and side sections which aredirectly secured to the enclosure 2 by fasteners which extend throughthe cover sections and holes provided in the flanges 2e, 2f and 2g.Cover 4 has a central opening 4b which is provided with a door 4cattached to the cover by a hinge 4d along the right-hand edge.

Prior to attaching the cover 4 to enclosure 2, an interior frameassembly is mounted to the rear panel 2a of the enclosure. A twininterior frame assembly is illustrated in FIG. 2. It comprises aleft-hand sheet metal pan 6 and a right-hand sheet metal pan 8 formed asa mirror image to pan 6 about the vertical centerline of the twin frameassembly. Pan 6 will be described in detail, with like alpha suffixesgiven to corresponding elements of pan 8. Referring also to FIG. 4, pan6 comprises an elongated, substantially planar member having an outersupport rail 6a formed over to extend forwardly along the left-hand edgeas viewed in FIG. 4 and an inner support rail 6b formed over to extendforwardly along the righthand edge. The outer end of each support rail6a and 6b has a right angle mounting flange extending toward the othersupport rail. Each flange is provided with a plurality of verticallyspaced, horizontally aligned holes 6c (FIG. 2). The free edge of theflange of support rail 6a also is provided with a plurality of notches6d spaced between the holes 6c.

A plurality of molded insulator supports 10 (FIGS. 2 and 4-7) areattached by screws 12 to the planar portion of pan 6 in end-to-endrelation to extend along the length of the pan. The specific number ofinsulators 10 to be provided on the respective panel varies according tothe desired size of the panelboard, that is, the number of devices ormounting increments desired. Referring to FIGS. 4-7, insulator support10 has three laterally spaced deep grooves 10a extending end-to-end andopen to the forward surface and the respective ends of the insulator.The forward surface is also provided with four forwardly projectingbarrier ribs 10b extending end-to-end of the insulator and disposed onlaterally opposite sides of grooves 10a. A pair of rearwardly extendinglateral flanges 10c define a base for the insulator and containclearance holes 10d (FIGS. 5 and 6) for receiving the screws 12therethrough. The latter are preferably thread cutting screws which takeinto holes (not shown) in the pan 6. A flat strip 14 (FIG. 2) ofinsulating material is affixed to pan 6 adjacent respective ends of thesupport insulators 10 to provide electrical insulation between the panand bus bars at the ends of the junctions of adjacent supports 10.

Three bus bars 16 are disposed within the respective aligned grooves 10aof supports 10. Bus bars 16 extend over the entire length of theadjacent support insulators 10. Bus bars 16 have holes 16a (FIG. 5)spaced along the length thereof to receive insulating bushings 18therein. The bushings extend to each side of the respective bus bar 16and may be provided with annular grooves for increasing the surfacedistance for electrical creepage protection. The upper surface ofinsulator 10 is provided with pockets 10e communicating with each groove10a. Pockets 10e are semi-cylindrically formed complemental to thebushings 18 and have tangential straight sides open to the forwardsurface of insulator 10 to permit insertion of bushings 18 therein fromthe front of the insulator. A transverse hole 10f is provided ininsulator 10 at each aligned group of pockets 10e, the hole 10f beingconcentric with the axis of the semi-cylindrical pockets and extendingentirely through the insulator from one lateral exterior surface to theother. The bus bars 16, with bushings 18 inserted within the respectiveholes 16a, are inserted into the respective aligned grooves 10a ofinsulators 10 such that the projecting ends of bushings 18 are receivedwithin pockets 10e. Subsequently, bolts 20 having a flat metallic washer22 and a rubber washer 24 disposed thereon adjacent the head of thebolt, are inserted through respective holes 10f and aligned holes 18a(FIG. 5) in bushings 18. A second flat washer 22 and rubber washer 24are placed over the projecting end of each bolt 20 and a nut 26 isthreaded thereon to clamp the walls of insulator 10 and bushings 18tightly together, securing bus bars 16 within the insulator 10. When soassembled, the forward edges of bus bars 16 are disposed between ribs10b (FIGS. 4 and 5) and recessed rearwardly from the forward edge of theribs to reduce the likelihood of conductive objects accidentallybridging the bus bars.

Referring to FIG. 2, a metal bracket 28 is attached across the flanges6a and 6b at the upper and lower ends thereof. Fiberboard insulators 30each having a rear, right-angled flange 30a attached to pan 6, extendforwardly to the respective bracket 28 at the upper and lower ends ofthe bus bar and insulator support assembly. Insulators 30 each have aforward flange 30b which overlies bracket 28 and is attached thereto.The insulators 30 electrically protect the ends of bus bars 16 fromaccidental contact by foreign conductive objects.

The interior frame assembly comprising pan 6 and the aforedescribedcomponents assembled thereto may be mounted within enclosure 2 when apanelboard having a single vertical row of switch, circuit breaker orlug unit components is desired. However, to increase the capacity of thepanelboard to accept a greater number of devices or a greater currentdistribution, a double, or twin interior frame assembly may be provided(such as that actually illustrated in FIG. 2) which will accept twoside-by-side vertical rows of plug-on devices or twin size devices whichextend across the twin interior. Moreover, the capacity to acceptadditional units may also be expanded by selecting an enclosure, coverassembly, and interior frame assembly which is longer than thatillustrated herein, and providing additional insulator supports 10 toaccommodate longer bus bars 16.

As hereinbefore mentioned, right-hand pan 8 is formed as a mirror imageto pan 6. It has an outer support rail 8a along the right-hand edgethereof and an inner support rail 8b along the left-hand edge thereof asviewed in FIG. 2, each rail containing holes 8c and the outer railhaving notches 8d corresponding to holes 6c and notches 6d. An insulatorsupport 10 and bus bar 16 assembly identical to that aforedescribed isattached to the flat planar portion of pan 8. Brackets 28 and fiberboardinsulators 30 are similarly attached to pan 8. To provide a twininterior frame assembly such as that shown in FIG. 2, the inner supportrails of pans 6 and 8 are bolted together along their length by bolts 34and nuts 36 extending through mating clearance holes in the respectiveinner rails (FIG. 4), thereby to establish a rigid, unitary assembly.

The flat planar portions of pans 6 and 8 extend upwardly beyond theupper ends of support rails 6a, 6b, 8a and 8b to provide a mountingsurface for a neutral connector assembly 36 (FIGS. 2 and 3). Thisneutral connector assembly comprises a left-hand connector plate 38 anda right-hand connector plate 40, each having a plurality of commerciallyavailable lugs arranged thereon. Plates 38 and 40 may be usedindividually with a respective pan 6 or 8 to provide a neutral connectorfor a single unit, or may be joined back-to-back by bolts 42 and nuts 44as seen in FIG. 3 to form a twin neutral connector unit 36 for the twininterior frame assembly of FIG. 2. Electrically insulating bushings 46are attached to the pans 6 and 8 by screws 48, and the plates 38 and 40are attached to the forward ends of bushings 46 by screws 50 to mountthe neutral connector 36 to the twin interior frame assembly. The wirereceiving openings of all of the lugs of neutral connector 36 aredirected toward the respective outer lateral edges of the interior frameassembly. Wires are brought into the panelboard through openings in thetop wall 2c located near the respective sidewalls 2b. Such wires thusrequire only a single ninety degree bend to be directed into theopenings of the lugs of neutral connector assembly 36, thereby reducingthe vertical wiring space necessary for wire bending at the end of theinterior frame assembly over embodiments in which the lug openings arevertically oriented which thereby require sequential ninety degree bendsto be received in the lug openings.

The interior frame assembly is mounted within enclosure 2 by fourcarriage bolts 52 (FIG. 4) which project forwardly through holes in therear panel 2a of the enclosure and are secured by nuts 54. Each pan 6and 8 is provided with clearance holes 6e and 8e (FIG. 2) at the fourcorners thereof. When a single interior frame assembly is utilized, itis placed over the carriage bolts 52 so that the pan rests against thenuts 54 and is secured thereto by nuts 56 threaded onto bolts 52. When atwin interior unit is utilized, the bolts 52 are arranged to projectthrough the holes 6e and 8e adjacent the respective edges containingouter rails 6a and 8a, and the holes adjacent the inner rails are notused. It is also possible to invert the interior frame assembly wherebythe neutral connector assembly 36 will be located at the bottom of thepanelboard when so desired.

A single interior frame panelboard may be connected to a source ofelectric power as an 800 amp panelboard. The twin panelboard illustratedin the drawings may be electrically connected as a 1200 amp panelboard.As shown in FIG. 8, a 1200 amp lug main twin unit 58 is attached to theinterior frame assembly across both outer support rails 6a and 8a. Lugmain unit 58 comprises a sheet metal enclosure having a pair of sides 60welded to a pair of mounting plates 61 at opposite ends. Mounting plates61 have inwardly directed flanges 61a to which a molded insulator block62 is mounted by screws 63. Three elongated U-shaped conductive straps64 having plug-on connectors at each end are mounted within insulatorblock 62 by screws 65. The ends of each strap 64 align with one of thebus bars 16 of pan 6 and a corresponding bus bar 16 of pan 8 toelectrically interconnect the respective corresponding bus bars of eachset when lug main unit 58 is plugged into place. Each conductor strap 64has a pair of wire receiving lug connectors 66 attached thereto forreceiving incoming electrical supply wires shown schematically in FIG.8. The forward edges of sides 60 are formed over at right angles toprovide flanges against which a sheet metal cover 67 is attached by aplurality of screws. The ends 67a of cover 67 project forwardly and haveoutwardly extending flanges 67b formed thereon to abut against theinterior surface of cover 4 when the latter is installed for reasonswhich will be described later in this description.

To facilitate mounting main lug unit 58 and other devices to thepanelboard, the panelboard is divided into increments determined by thepole-to-pole dimension of the molded case circuit breakers utilized onthe panelboard. This dimension is herein referred to as "x". Withreference to FIG. 2, the vertical spacing between adjacent notches 6dalong support rail 6a is "x", as is the spacing between adjacent holes6c along rails 6a and 6b. The lug main unit 58 requires a 7x space, i.e.the vertical dimension of the enclosure from one side member 60 to theother is equal to seven of the x increments. The rear edges of sidemembers 60 are provided with slots 69 for receiving support rails 6a and8a at respective notches 6b and 8b, thereby to provide a means oflocating a device such as the plug-on lug main unit 58 on the interiorframe assembly when installing the device.

To further facilitate mounting of lug main unit 58 and other devices tothe panelboard, each device is provided with at least one latch assembly70. Twin size devices such as lug main unit 58 which extend across theentire width of a twin interior frame assembly from rail 6a to rail 8aare provided with a latch assembly 70 at each end. Devices which mountonly to a single interior frame assembly, or to only one panel 6 or 8 ofthe twin interior frame assembly, have a single latch 70 as will be seenin later description. The details of latch assembly 70 are more clearlyshown in FIGS. 14-16. Referring specifically to FIG. 14, the right-handend of lug main unit 58 is shown in enlarged detail. A portion of sidemember 60 is broken away to the right of slot 69, showing mounting plate61 in cross-section. FIG. 15 shows the latch assembly 70 when viewedfrom the back, or underside with respect to the orientation of FIG. 14,as represented by lines 15--15 in FIG. 14.

Latch assembly 70 comprises a T-shaped mounting bracket 71 which isattached against the flat surface of mounting plate 61 by a pair ofscrews 72. The outer ends of the cross bar portion of T-shaped mountingbracket 71 are formed over at right angles to provide depending ears71a. An operating bracket 73 is pivotally mounted between the ears 71aby a pair of riveted pins 74. As viewed from the underside in FIG. 15,the operating bracket 73 is a shallow U-shaped channel member. Theopposite legs 73a of bracket 73 are pivotally connected to the ears 71anear the upper ends of the respective legs by the pins 74, and extenddownwardly along the outer surface of rail 8a. The lower end of eachopposite leg 73a has an inwardly directed hook 73b formed thereon, thelower inward corner of which is beveled to serve as a cam surface aswill later be described. An integrally formed release arm 73c extendsangularly away from the central portion of bracket 73 to projectoutwardly and angularly away from bracket 71 and mounting plate 61. Aheaded pin 75 is inserted through an elongated slot 73d in release arm73c and through a hole (not shown) in a recessed portion of mountingbracket 71. The upper end of pin 75 is riveted over prior to attachmentof the latch assembly 70 to mounting plate 61 to retain pin 75 assembledto bracket 71. Attachment of the latch assembly 70 to mounting plate 61traps the riveted-over end of pin 75 between plate 61 and the recessedportion of bracket 71. A helical compression spring 76 is disposed overthe shank of pin 75 between bracket 71 and release arm 73c to bias hook73b toward rail 8a.

To attach plug-on lug main unit 58 to the interior frame assembly, aninstaller may grasp the mounting plates 61 at each end of the unit andposition the rear edges of sides 60 against the rails 6a and 8a suchthat slots 69 align with corresponding pairs of notches 6d and 8d. Thesides 60 may rest on the lower surfaces of the respective notches, asseen in FIG. 15, thereby accepting the weight of the device. Theinstaller then pushes the unit inwardly to engage the plug-on connectorsof straps 64 with the respective bus bars 16. In so doing, the camsurfaces of hook portions 73b of the latch assemblies 70 engage therounded outer corner of support rails 6a and 8a to cam the operatingbrackets 73 against the bias of springs 76. As best seen in FIGS. 14 and16, support rails 6a and 8a are provided with a plurality of slots 6fand 8f in the forwardly extending legs thereof which receive hookportions 73b when the upper or forward ends of slots 69 seat firmlyagainst the forward flanges of support rails 6a and 8a. When the hookportions 73b snap into the slots 6f and 8f, the installer knows that theunit is properly and fully attached to the interior frame assembly.Moreover, the hooks retain the unit in this fully attached position. Tolock the unit to the interior frame, a bolt 77 is threadably insertedinto a tapped hole in each mounting plate 61 and is advanced inwardlyuntil the end abuts the upper surface of release arm 73c to prevent theoperating bracket from being rotated away from the respective supportrail to withdraw the hook portions 73b from slots 6f and 8f. Bolt 77 maybe threaded outwardly of mounting plate 61 and away from release arm 73cwhen it is desired to remove the unit from the interior frame assembly,and the installer may then release the hook portions 73 b by graspingthe underside of release arm 73c together with mounting plate 61 androtating the operating bracket 73 to release the hook portions 73b bypulling outwardly on the release arm and the mounting plate 61.

Referring to FIGS. 1 and 9, a single, three-pole molded case circuitbreaker 78 is mounted in the segment immediately above lug main unit 58.Circuit breaker 78 may, by example, be a 600 volt, 100-225 amp breaker,however the details of the breaker are not significant to thisinvention. To conserve vertical mounting space on the panelboard,circuit breakers are not mounted within a metal enclosure similar tothat of the enclosed fusible switch devices to be described later, butinstead are provided with a mounting assembly for attaching the breakerdirectly to the interior frame assembly. A mounting assembly for breaker78 comprises a mounting plate 79 having a first pair of depending sides79a and a second pair of depending sides 79b (only one of each of thesides being visible in FIG. 9) spaced from sides 79a to form a slot 79csimilar to slot 69 (FIG. 8) between the respective adjacent sides. Theupper surface of mounting plate 79 is stepped upward in the area of theforward flange of support rail 8a to raise the forward surface of thebreaker 78 to a predetermined depth with respect to the front of thepanelboard. The left-hand end of mounting plate 79 (as viewed in FIG. 9)has a depending leg terminating in a right-angle flange 79d. Aninsulating molding 80 is attached to flange 79d by screws 81. Molding 80provides support and electrical isolation for three conductor straps 82which are electrically secured to terminals of breaker 78. Straps 82 areof different lengths and are formed downwardly away from the breaker attheir unsecured ends to align with respective ones of the bus bars 16 inpan 8. Screws 83 secure the longer two of the three straps 82 toinsulating molding 80 to provide additional support for the straps. Theunsecured ends of straps 82 are provided with plug-on connectors forengaging bus bars 16. Mounting plate 79 and attached molding 80 areattached to the rear surface of circuit breaker 78 by pairs of screws 84and 85, respectively, which extend through holes in the molded case ofcircuit breaker 78. Screws 84 extend through holes in mounting plate 79to receive nuts on their projecting ends. Screws 85 extend into holes inmolding 80 and threadably engage tapped inserts in the molding. Screws84 also secure a filler plate support bracket 86 to the front surface ofbreaker 78. An L-shaped filler plate 87 having a forwardly projectingouter end 87a which terminates in a right angle flange 87b is pivotallyattached to support bracket 86 adjacent the inner end of bracket 86. Ascrew 88 is inserted through a hole in end 87a to threadably engage analigned hole in a flange of bracket 86 to secure the filler plate 87 inposition on the bracket. Screws 85 also secure a center filler platesupport bracket 89 to the forward surface of breaker 78. A latchassembly 70 is attached to mounting plate 79 in the manner describedabove in conjunction with mounting plates 61.

Breaker 78, being a three-pole device, requires a 3x segment on theinterior frame assembly. The breaker is plugged onto the interior frameassembly by grasping the mounting plate 79 and the opposite end of thebreaker, aligning the respective slots 79c with a notches 8d in supportrail 8a one of which is partially occupied by the side member 60 of lugmain unit 58, as seen in FIG. 15, and another notch 8d located threeincrements above the unit 58. The width-of notches 8d are made toaccommodate the thickness of material of two mounting plates or sideplates. The breaker 78 is then pushed onto the interior frame until theforward end of slot 79c firmly seats against the forward flange ofsupport rail 8a whereupon the hooks 73b of latch 70 snap into thecorresponding slots 8f of support rail 8a and the left-hand end ofinsulating molding 80 rests upon inner support rail 8b. Screws 90 extendthrough holes in the left-hand end of molding 80 to thread intorespective holes 8c in the forward flange of rail 8b to secure that endof-the breaker unit, and screws 77 (FIG. 14) may be threaded inwardly tolock the latch end of the unit in place.

The space on panel 6 immediately across from circuit breaker 78 isunoccupied in the exemplary embodiment illustrated in the drawings. Acenter filler plate 91 is attached to bracket 89 by a pair of screws 92.Another filler plate 93 is attached to the free end of center fillerplate 91 by another pair of the screws 92 and to a pair of forwardlyprojecting Z-shaped brackets 94 by a pair of screws 95. Brackets 94 aremounted on the forward flange of support rail 6a. The outer end offiller plate 93 has a forwardly projecting leg 93a which terminates in aright angle flange 93b. Filler plates 91 and 93 have rearwardlyextending sides 91a and 93c, respectively, for closing off the spacewhen adjacent devices have a greater panel depth from cover 4.

Referring to FIGS. 1 and 10, another arrangement of circuit breakers isprovided in the segment immediately above circuit breaker 78. In FIG.10, the left-hand pan 6 has a 240 volt, 100-225 amp type CHH molded casecircuit breaker 96 mounted thereon, while the right-hand pan 8 has a 240volt, 100-225 amp type CC molded case circuit breaker 98 mountedthereon. These breaker unit assemblies are similar to breaker 78 in thatthey each are mounted to a support assembly comprising molding 80 andmounting plate 79 in the manner aforedescribed except that breaker 98,being somewhat shorter than breakers 78 and 96, has both ends attachedto molding 80 by respective screws 84 and 85. The hinged filler plates101 and 102 for this pair of breakers are also different from that forbreaker 79. Z-shaped brackets 99 are mounted on the forward surface ofeach mounting plate 79 in aligned pairs with only the near side bracketsbeing visible in FIG. 10. The support brackets 100 for the hinged fillerplates 101 and 102, respectively, of breakers 96 and 98 do not extendfully to the outside of the panel as did support bracket 86. Thus, thefiller plates 101 and 102 are hingedly supported by brackets 100adjacent their respective inner ends and are secured to the forwardflanges o brackets 99 by screws 103 adjacent their outer ends. The outerends 101a and 102a, respectively, of filler plates 101 and 102 extendforwardly and terminate in right angle flanges 101b and 102b,respectively. Breakers 96 and 98 are individually mounted to theinterior frame assembly in the manner aforedescribed in conjunction withcircuit breaker 78. Both breakers require 3x segments on the panelboard.When so assembled, a center filler plate 104 is secured to center fillerplate brackets 105 which are attached to the respective breakers byscrews 85. Breakers 96 and 98 have less height than breakers 78 andtherefore center filler plate 104 is elevated above the surface of thebreakers to maintain a common level between the filler plates 92 and104. Each of the filler plates 101, 102 and 104 has pairs of rearwardlyextending sides 101c, 102c and 104a respectively, for accommodatingdifferent panelboard depths of adjacent devices.

Referring next to FIGS. 1 and 11, a 600 volt, 400 to 800 amp type Mmolded case circuit breaker 106 is mounted in the next available segmentabove circuit breakers 96 and 98. In view of the physical size of thisbreaker, it is arranged as a twin unit, attaching to both support rails6a and 8a. In view of the electrical capacity of breaker 106, it isarranged to plug onto both sets of bus bars 16 in electrical parallel. Amolding 107 is attached to the underside of breaker 106 by screws 108which extend through recessed holes in the molded case of breaker 106and take into threaded inserts in molding 107. Molding 107 providessupport and electrical isolation for three conductive straps 109 whichare connected to the respective terminals of the three-pole breaker. Theends of straps 109 are formed down to be in alignment with therespective bus bars 16 of left-hand pan 6 and each have plug-onconnectors attached thereto for making electrical connection with thosebus bars. Short conductive straps 110 are attached to straps 109, theends of which are turned down to be in alignment with a respectivecorresponding bus bar 16 of right-hand pan 8. The ends of straps 110have plug-on connectors attached thereto for making electricalconnection with the respective last mentioned bus bars. When mounted tothe interior frame assembly, the respective straps 109-110 and theirattached connectors afford a parallel electrical connection fromcorresponding bus bars of each set thereof to a respective terminal ofthe breaker. As may be seen in FIG. 11, breaker 106 is mountedoff-center with respect to the twin interior frame assembly.Accordingly, two separate mounting plates 111 and 112 are utilized withthis breaker. Mounting plate 111 has a first pair of sides llla and asecond pair of sides lllb spaced lengthwise of the unit to define a slotlllc for receiving the support rail 6a at respective notches 6d. A latchassembly 70 is attached to the mounting plate 111 at the left-hand endthereof as viewed in FIG. 11. The right-hand end of mounting plate 111has a depending leg which terminates in a right-angle flange llld whichattaches to molding 107 by screw 113. Mounting plate 112 has a firstpair of short side members 112a and a second set of side members 112bspaced lengthwise of the unit to define a slot 112c for receiving thesupport rail 8a at respective notches 8d. A latch assembly 70 isattached to support plate 112 at the right-hand end thereof as viewed inFIG. 11, and the left-hand end thereof is provided with a depending legterminating in a right-angle flange 112 d which is attached to molding107 by screw 114. Two pairs of elongated C-shaped brackets 115 areutilized with this unit, a first pair being located in spaced, laterallyaligned relation and secured to mounting plate 112 so that only the nearside bracket is visible in FIG. 11. The second pair is attached tomounting plate 111 in spaced, but laterally staggered relation. A fillerplate 116 is attached directly to the front surface of breaker 106 byscrews 117 at the left-hand end thereof and to the forward flanges ofbrackets 115 by screws 118. Filler plate 116 has a forwardly projectingend 116a terminating in a right-angle forward flange 116b and rearwardlyextending sides 116c. Another filler plate 119 is attached directly tothe front surface of breaker 106 by screws 120 and to the forwardflanges of brackets 115 by screws 121. Filler plate 119 has a forwardlyprojecting end 119a terminating in a right-angle forward flange 119b andrearwardly extending sides 119c.

Breaker unit 106 is attached to the twin interior frame assembly in themanner aforedescribed in conjunction with lug main unit 58 so as tocause the hooks 73b of both latch assemblies 70 to engage the respectiveslots 6f and 8f of support rails 6a and 8a. When so engaged, the molding107 rests upon the inner flanges 6b and 8b to provide additional supportfor the unit.

Referring to FIGS. 1 and 12, two additional types of devices are shown.The device on the left in FIG. 12 is a three-pole lug unit 122 whereinunprotected electric power may be taken from the panelboard anddistributed via wiring to another panelboard, protected device or thelike. Lug unit 122 comprises a pair of side plates 123, the near sidebeing partially broken away to show an insulator 124, conductive strap125 and connector lug 126 of one pole. Side plates 123 are joined inspaced relation by a mounting plate 127, similar to mounting plate 61,to which the side plates are welded at their lower left-hand corner, apair of upper braces 128 welded between the side plates at the oppositeupper corners, and a lower brace 129 welded between the side plates atthe lower right-hand corners of the side plates. Three separateidentical insulators 124 are used in the lug unit 122, each attached atone end to a flange 127a of mounting plate 127 by screws 130 and at theopposite end to lower brace 129 by screws 131. An L-shaped conductivestrap 125 is secured to the insulator 124 by a pair of screws 132, onlyone of which is shown in FIG. 12. The short leg of strap 125 dependsthrough one of three openings in insulator 124 and in alignment with oneof the bus bars 16. Similarly to the previously described devices, thedepending leg of strap 125 has a plug-on connector attached thereto forelectrical connection with the bus bar. The longer two of the threestraps 125 are further provided with L-shaped support brackets 133attached to the depending leg and extending across the upper surface ofinsulator 124. Screws 134 secure the brackets 133 to the insulator 124.Each conductive strap 125 is provided with a pair of upstanding screws135 for securing the wire connector lug 126 thereto. A cover 136 havinga forwardly extending end 136a and a right-angle forward flange 136b isattached to the top of lug unit 122 by screws 137 located at therespective corners of the cover and which take into openings in theupper braces 128. A latch assembly 70 is attached to mounting plate 127.Sides 123 are provided with slots 123a similar to slots 69 in FIG. 8,for receiving support rail 6a at respective notches 6d.

Lug unit 122 is an 8x unit, that is, it requires eight increments alongthe vertical dimension of the support rail for mounting purposes. As maybe seen in FIG. 1, lug unit 122 is not mounted immediately adjacentcircuit breaker 106 but is spaced one x increment above that breaker. Asingle increment filler plate 138 is mounted in the space between lugunit 122 and circuit breaker 106, the filler plate 138 being similar tofiller plate 93 shown in FIG. 9 except that an additional bracket isrequired to be mounted on inner support bracket 6b to support the innerend of filler plate 138. The mounting details of this filler plate havenot been specifically shown. Lug unit 122 is mounted in theaforedescribed manner and the right-hand or inner end is attached toinner rail 6b by a pair of screws extending through the outermost twoinsulators 124 and lower brace 129 to be received in holes 6c in theforward flange of rail 6b.

A three-pole 30 amp enclosed fusible switch 140 is mounted on right-handpan 8 in FIG. 12 across from lug unit 122. Switch 140 comprises a pairof sides 141 welded to a mounting plate 142. Unlike previously describedmounting plates, the plate 142 extends fully across the bottom of switch140. The left-hand or inner end of mounting plate 142 has a dependingleg which terminates in a flange 142a. A cross-brace 143 is weldedbetween sides 141 at the upper right-hand corner and a secondcross-brace 144 is welded between the sides 141 at the upper left-handcorner. A hinged cover 145 is attached to the enclosure by securing oneleg of the hinge to brace 143 by a plurality of screws 146. An upwardlyprojecting bracket 147 having a forward flange 147b is also attached tobrace 143 at the exterior of the enclosure. A latch assembly 70 isattached to mounting plate 142 at the outer or right-hand end. Sides 141have slots 141a formed therein similar to slots 69 to receive supportrail 8a at respective notches 8d. A molding 148 is attached to theunderside of mounting plate 142 by screws 149. Insulator 148electrically isolates and supports three conductive straps 150 leadingfrom terminals of a three-pole disconnect switch 151, the details ofwhich have not been shown. Each of the straps 150 are formed downwardlyat one end in alignment with the respective bus bars 16 of pan 8 andhave plug-on connectors attached thereto for making electricalconnection with the bus bars.

Switch 140 requires a 5x segment along the vertical dimension of theinterior frame assembly. As may be seen in FIG. 1, switch 140 is spacedabove the circuit breaker 106 by a 3x segment, and the spacetherebetween receives a 3x wide filler plate 152 mounted on rails 8a and8b in the same manner as described for filler plate 138. Switch 140 ismounted to the interior frame assembly in the aforedescribed manner,with the flange 142a being secured to the forward flange of rail 8b byscrews 153.

Referring to FIG. 1, a 60 amp three-pole enclosed fusible switch 154 ismounted immediately above lug unit 122, this switch requiring a 5xsegment on the interior frame. A 100 amp, three-pole enclosed fusibleswitch 156 is mounted across from switch 154 immediately above switch140, this switch requiring a 6x segment on the interior frame. Apartfrom the relative size and rating differences in these devices, switches154 and 156 are essentially identical to switch 140 and have not beenshown separately. Switch 154 is provided with a blown fuse indicatordevice 155 mounted to the front cover thereof. The blown fuse indicator155 is like that described and claimed in copending application Ser. No.748,106 filed June 24, 1985 in the names of Michael A. Damiano andRichard F. Schmerda entitled "Open Circuit Indicator" and assigned tothe assignee of this invention. Indicator 155 provides an illuminatedidentification of the specific fuse in switch 154 which is blown whensuch fault occurs.

With reference to FIGS. 1 and 13, a 200 amp, three-pole twin sizeenclosed fusible switch 158 is mounted immediately above switches 154and 156. This unit is similar to switches 140, 154 and 156 except thatit occupies the entire width of the twin interior frame assembly. Itcomprises a pair of sides 159 welded along their bottoms to a mountingplate 160 which extends for the full length of the unit. A pair of crossbraces 161 identical to braces 146 are welded between sides 159 atopposite upper corners thereof. A pair of hinged covers 162 and 163 arerespectively attached to the cross braces and upright brackets 164 and165 having forward flanges 164b and 165b are also attached to theexterior of the cross braces in the same manner as cover 145 and bracket147 are attached to brace 143. An insulator 166 is attached to theunderside of mounting plate 160 by screws 167 to support andelectrically isolate conductive straps 168 leading from a three-poledisconnect switch 169. A pair of latch assemblies 70 are attached to themounting plate 160 at the respective ends thereof. Switch unit 158requires a 7x segment along the interior frame assembly and is installedin the manner aforedescribed in conjunction with twin size devices suchas lug main unit 58 and circuit breaker 106.

As seen in FIG. 1, the interior frame assembly of the panelboard of thisinvention will accept a flexible arrangement of plug-on devices. It ispreferable that circuit breakers of the same x increment requirement bemounted across from each other, and that circuit breakers not be mountedacross from enclosed fusible switch devices or lug devices. Whenseparate enclosed switch devices or lug units are mounted across fromeach other, their vertical dimension along the panelboard does not needto be equal. Each device is provided with at least one forwardlyprojecting leg and right angle forward flange such as 67a-67b, 87a-87b,93a-93b, 101a-101b, etc., to form a dead front barrier around theperiphery of the panelboard when the cover 4 is assembled to theenclosure 2. To complete the dead front barrier at the ends of theinterior frame assembly, covers 170 and 171 are provided as seen in FIG.1 and in FIGS. 17 and 18, respectively, and described hereinbelow.

In FIG. 17, a lower cover 170 is viewed from the bottom of the interiorframe assembly. A pair of elongated C-shaped brackets 172 are attachedto the brackets 28 by screws 173. Cover 170 has a Z-shaped cross sectioncomprising an upper rearwardly extending flange 170a, a vertical centralleg 170b and a lower forwardly extending flange 170c. The ends ofvertical leg 170b have forwardly extending arms 170d terminating inforward right angle flanges 170e which align with the forward flanges ofthe respective plug-on devices. Screws 174 secure the cover 170 to theforward ends of brackets 172.

Upper cover 171 is shown in transverse cross-section in FIG. 18. Itcomprises a Z-shaped cross-section having a lower rearwardly extendingflange 171a, a vertical leg 171b and an upper forwardly extending flange171c. The ends of vertical leg 171b have forwardly extending arms 171dterminating in a forward flange 171e, only one of which appears in FIG.18. Cover 171 is attached to the interior frame assembly by a first pairof elongated C-shaped brackets 176 attached to upper brackets 28 byscrews 177 and to the vertical leg 171b by screw 178. A second pair ofelongated C-shaped brackets 179 are attached to the rear portions ofpanels 6 and 8 by screws 180 and to the vertical leg 171b of cover 171by screws 181.

As may be seen in comparing FIGS. 9, 10 and 11 with each other and withFIGS. 8, 12 and 13, the circuit breaker units have varying depths fromthe front surface of the panelboard to the front surface of therespective units, while the enclosed switches and lug units have auniform depth. The differences in heights are effectively closed-off toprovide dead front protection by the side flanges of adjacent fillerplates and enclosed switch units and the rearwardly projecting flanges170a and 171a of lower and upper covers 170 and 171.

With reference to FIG. 19, when a single interior frame assembly is usedand therefore only a single row of plug-on devices is provided, noforwardly projecting end structure is provided at what would be theinner end of such device on a twin interior frame assembly. In thisinstance, cover 4' in FIG. 19 is provided with a rearwardly extendingflange 4e attached along the vertical edge of door opening 4b'. FIG. 19shows a single interior frame assembly having a circuit breaker devicesuch as circuit breaker 96 attached thereto in the foreground and anenclosed fusible switch device such as switch 154 shown in thebackground. Flange 4e extends along the right-hand end of switch 154closely adjacent the ends of the cover and sides thereof, and similarlyextends along the ends of any enclosed lug units that may be mounted onthe panelboard. Flange 4e abuts the upper surfaces of filler plates suchas 104 of circuit breaker device 96 and any other filler plate that maybe used in such installation. In this manner, flange 4e cooperates withthe forwardly extending end structures of the respective plug-on devicesto provide a dead front for a single interior frame panelboard.

While the foregoing has described the power distribution panelboard ofthis invention in preferred embodiments, it is understood that it issusceptible to further arrangements and various modifications withoutdeparting from the scope of the appended claims.

We claim:
 1. A power distribution panelboard comprising:a panel havingforwardly extending mounting rails disposed along opposed vertical sidesthereof, at least one of said rails having locating means defining apredetermined number of adjacent vertical mounting increments along saidrails; a plurality of like insulator members each having a lengthcorresponding to a multiple of said mounting increments mounted to saidpanel between said rails in contiguous end to end relation defining acombined length equal to a combined height of said predetermined numberof mounting increments, each of said insulators having a plurality ofgrooves in a forward surface extending between opposite ends formingcontinuous grooves extending over said combined length of said pluralityof insulator members; a plurality of bus bars having respective lengthssubstantially equal to said combined length of said plurality ofinsulator members respectively disposed in said continuous grooves; anda plurality of devices from a group comprising enclosed lug connectordevices, enclosed fusible switch devices and non-enclosed molded casecircuit breakers mounted across said mounting rails transversely theretoin variably selectable combinations and arrangements, each of saiddevices having a height corresponding to a multiple of said mountingincrements and means cooperable with said locating means positioning arespective device on a multiple increment segment of said panelcorresponding to the height of said respective device, each said deviceeffecting plug-on electrical connection to said bus bars with saiddevice seated firmly against said mounting rails, and one of saiddevices being a main device having electrical power supply wiresconnected thereto electrifying said bus bars through its respectiveplug-on electrical connection.
 2. The panelboard defined in claim 1wherein a major portion of said bus bars is received within respectiveones of said grooves, and said insulator members have forwardlyprojecting barriers on opposite sides of each bus bar extending beyondforward edges of said bus bars.
 3. The panelboard defined in claim 1wherein:said insulator members have transversely aligned holes throughwalls thereof defining said grooves, and pockets in said wallscommunicating with said grooves and being open to said forward surface,said pockets being concentric with said aligned holes; said bus barseach having a plurality of holes therethrough disposed in alignment withsaid aligned holes in each of said insulator members; insulatingbushings having holes therethrough disposed within each hole in said busbars, said bushings being received in respective ones of said pockets;and fastener means extending through respective sets of transverselyaligned holes in respective ones of said insulator members and throughsaid holes in said insulating bushings to opposite exterior surfaces ofsaid insulator members retaining said bus bars within said grooves andlimiting outward movement of said walls upon the occurrence of shortcircuit currents in said bus bars.
 4. The panelboard defined in claim 3wherein said fastener means compresses said walls and said bushingstogether.
 5. The panelboard defined in claim 3 wherein said fastenermeans comprises bolts extending through said insulator members and saidbushings with respective heads of said bolts at one exterior surface ofsaid insulator members and nuts engaged with said bolts at the otherexterior surface of said insulator members, and resilient meansinterposed with said heads and said nuts and respective exteriorsurfaces of said insulator members for permitting limited flexure ofsaid walls of said insulator members.
 6. A power distribution panelboardcomprising:a panel having a pair of mounting rails individually disposedalong opposite vertical sides thereof; insulator means mounted to saidpanel between said rails; first and second sets of bus bars supported bysaid insulator means, said bus bars being disposed between said railsand parallel thereto; a plurality of devices from a group comprisingenclosed lug connector devices, enclosed fusible switch devices andmolded case circuit breaker devices mounted to said panel, at least someof said devices being twin devices mechanically attached to both saidrails and plug-on connected to both said first and second sets of busbars, and one of said twin devices being connected to an electric powersupply, conjointly electrifying respective bus bars of said first setand corresponding bus bars of said second set in electrical parallel bymeans of its plug-on electrical connection with said first and secondsets of bus bars.